This invention relates to a prosthetic leg with a multi-axis knee joint applied with a link mechanism, and more particularly to a multi-axis knee joint having an extension auxiliary mechanism for preventing immediate bending of the knee joint when the prosthetic leg is in its stance phase.
In general, a prosthetic leg with a knee which can be bent and extended, includes an upper thigh member to which a load of a wearer is applied through the thigh, a lower thigh member supporting on its lower end a leg member, and a knee joint for connecting the upper thigh member to the lower thigh member. There are two types of knee joints, one being a single-axis type which has a single rotational axis and the other being a multi-axis type which is applied with a link mechanism. When the knee is bent and extended, the single rotational axis itself in the single-axis knee joint is normally served as the center of rotation. In contrast, in the multi-axis knee joint, the position of the center of rotation (or instantaneous center) is varied in accordance with bend and extension of the knee. This variation in the center of rotation is desirable in respect of providing a natural and beautiful walking style (i.e., walking attitude).
Incidentally, when a prosthetic leg is designed, it is important that a countermeasure is provided to prevent immediate bend of the knee in the stance phase. In this respect, since the single-axis knee joint is comparatively simple in structure, a load brake for generating a braking force when a load of the wearer is incurred to the prosthetic leg, can be disposed around the rotational axis. In contrast, in the multi-axis knee joint, since at least two front and rear links are essentially employed one at the front side of the knee and the other at the rear side of the knee, it is difficult to install a load brake on the knee portion. In the extended state of the knee, however, an instantaneous center, in the multi-axis knee joint, is located at an area near the crotch joint which is situated upwardly of the actual knee portion. For this reason, the person wearing the multi-axis type prosthetic leg can easily maintain a stable state of the knee by a so-called voluntary control operation.
The extension auxiliary mechanism according to the present invention renders a force for extending the knee to such a multi-axis knee joint and it is a mechanism effective for preventing immediate bend of the knee. U.S. Pat. No. 4,310,932 (corresponding to Japanese Patent Examined Publication (Kokoku) No. Sho 61-44504) and U.S. Pat. No. 4,911,709 (corresponding to Japanese Patent Unexamined Publication (Kokai) No. Sho 62-295658) disclose prosthetic legs with an extension auxiliary mechanism using a coiled spring with respect to the multi-axis type prosthetic leg. In those extension auxiliary mechanisms, however, there is provided not only the function for preventing immediate bend of the knee in the stance phase but also the function for assisting bending of the knee joint at a large angle in the swing phase.
In order to control the prosthetic leg with a high degree of precision, it is desirable to be capable of making a control of the leg in the swing phase and making an immediate knee bend prevention control in the stance phase separately or independently. By doing so, a more appropriate control can be made in accordance with a walking speed. The controlling technique itself in the swing phase is well known. For example, U.S. Pat. No. 5,344,446 (corresponding to Japanese Patent No. 2501346) discloses a technique for making a control using an air-cylinder device such that an opening degree of a valve in the cylinder varies in accordance with a walking speed.
The present invention has been accomplished under such a basic technical concept that the prevention of the immediate bend of the knee portion in the stance phase and the control in the swing phase should be made independently.